Crystalline carbon had never been found in nature until now

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Researchers using a diamond paste to polish a slice of meteorite stumbled onto something remarkable: crystals in the rock that are harder than diamonds.

A closer look with an array of instruments revealed two totally new kinds of naturally occurring carbon, which are harder than the diamonds formed inside the Earth.

"The discovery was accidental but we were sure that looking in these meteorites would lead to new findings on the carbon system," said Tristan Ferroir of the Universite de Lyon in France.

Ferroir is the lead author of a report in the new diamond in the Feb. 15 issue of the journal Earth and Planetary Science Letters.

The researchers were polishing a slice of the carbon-rich Havero meteorite that fell to Earth in Finland in 1971. When they then studied the polished surface they discovered carbon-loaded spots that were raised well above the rest of the surface — suggesting that these areas were harder than the diamonds used in the polishing paste.

"That in itself is not surprising," said diamond researcher Changfeng Chen of the University of Nevada in Las Vegas. He explained that sometimes during the shock of impact graphite can create jumbled "amorphous" zones that can resist diamonds, at least those coming at them from one direction.

But what apparently happened in the Havero meteorite is that graphite layers were shocked and heated enough to create bonds between the layers — which is exactly how humans manufacture diamonds, Chen explained.

Ferroir's team took the next step and put the diamond-resistant crystals under the scrutiny of some very rigorous mineralogical analyzing instruments to learn how its atoms are lined up. That allowed them to confirm that they had, indeed, found a new "phase" or polymorph of crystalline carbon as well as a type of diamond that had been predicted to exist decades ago, but had never been found in nature until now.

"The new structure is very interesting," Chen told Discovery News. "It gives us some clues so we can try to make it in the laboratory, and then investigate it."

Among the things that would be interesting to learn, Chen said, is how hard are the new kinds of diamonds. The sample from the meteorite was far too small to test for hardness, except to show that it is certainly harder than regular diamonds.

"The only evidence we have for a higher hardness than diamond is the fact that we polished the rock section with a diamond paste and that our polymorph and polytypes were not polished by this material," said Ferroir. "This why we do think that its hardness is harder than diamond."

However, there is no way at the present to compare them to the artificial ultra-hard diamonds known as lonsdaleite and boron nitride, Ferroir said.